1. Field of the Invention
The present invention relates to an optical disc device and an optical information recording method and is suitably applied to, for example, an optical disc device that records information on a recording medium using a light beam.
2. Description of the Related Art
An optical disc device that uses an optical disc as an information recording medium is wide spread. In general, as the optical disc, a CD (Compact Disc), a DVD (Digital Versatile Disc), a Blu-ray Disc (registered trademark; hereinafter referred to as BD), and the like are used.
Among such optical discs, there is a multilayer disc DC having plural signal recording layers SR that reflect a light beam at predetermined reflectance as shown in FIG. 1A. An optical disc device corresponding to such a multilayer disc DC reads out address information recorded in the signal recording layers SR in advance to thereby irradiate a light beam Lm on a desired track on which the light beam Lm should be irradiated in the signal recording layer SR.
In general, an optical disc device records, on an optical disc, various contents such as music content and video content or various kinds of information such as various data for a computer. In particular, in recent years, since an amount of information increases because of high definition of videos and high sound quality of music and an increase in the number of contents recorded on one optical disc is requested, there is a demand for a further increase in capacity of the optical disc.
In the multilayer disc DC described above, it is possible to increase a storage capacity thereof by increasing the number of signal recording layers SR. However, in this optical disc DC, it is necessary to multilayer the signal recording layers SR by sequentially stacking intermediate layers SM present among the signal recording layers SR. There is a limit in the increase in capacity in terms of manufacturing when it is taken into account that yields in the respective layers are integrated.
Therefore, as one method of increasing a capacity of the optical disc, there is proposed an optical disc device that forms plural recording marks RM in a thickness direction in a uniformly-formed recording layer 101 to record information as shown in FIG. 1B (see, for example, JP-A-2007-220206 (FIGS. 1, 4, and 5)).
In an optical disc 100 corresponding the optical disc device having such a configuration, it is assumed that recording marks are formed on imaginary tracks TR in the recording layer 101 as shown in FIG. 2A. However, since the recording layer 101 is uniform, there is nothing that can mark positions in the recording layer 101. In the following explanation, for convenience of explanation, it is assumed that the plural imaginary tracks TR present in the thickness direction are connected in a cylindrical shape as shown in FIG. 2B.
Therefore, in the optical disc 100, as shown in FIGS. 1B and 2A, a servo layer SS in which tracks are formed is separately provided. The recording marks RM are formed in desired places in the recording layer 101 with the servo layer SS set as a reference position in the thickness direction in the optical disc 100.
The optical disc device focuses, for example, a red light beam Lr having the wavelength of 660 [nm] on the servo layer SS and focuses a predetermined blue light beam Lb having the wavelength of 405 [nm] on a position shifted from a focus Fr of the red light beam Lr by predetermined depth d. Consequently, the optical disc device irradiates the blue light beam Lb on a target mark position present at the predetermined depth d from the servo layer SS in which the focus Fr of the red light beam Lr is located.